For healthy human mothers otherwise not exposed to contaminating environmental pollutants or toxins, mother's milk constitutes the best food for full-term, vigorous human infants. Unfortunately, most infants are not breast fed at all, or if breast fed, not for an adequate period of time. In the United States and other developed nations, surveys show that even during a time when the percentage of mothers choosing to breast-feed rose from 25% to 35%, less than one-tenth of those mothers continued to breast-feed beyond three months (U.S. Department of Health, Education and Welfare (1979), "Trends in Breast-Feeding Among American Mothers", DHEW Publication No. (PHS) 79-1979, National Center for Health Statistics, Hyattsville, Md.). If second births are considered, the percentage of breast-fed infants in all categories is reduced even further. Consequently, a large majority of American mothers still rely on bottle feeding, either of infant formula or some other substitute for breast milk. Presently, commercially available human infant formula used to replace mother's milk is based primarily upon the protein constituents of cow's milk. These infant formula compositions have led to difficulties in terms of nutrient balance, bioavailability of nutrients and sensitivity of human infants to non-human/animal protein. Specifically, allergic reactions to the non-human animal protein used with these infant formulas caused a change in the protein component of the commercially available formula to soy-protein based formulas, although many infants that are allergic to cow's milk are also allergic to soy-based milks (Am. Acad. of Pediatrics Comm. on Nutrition, Pediatrics, 72, 359-363 (1983)).
Additionally, many of the problems with the use of cow's milk protein are associated with difficulties in digestibility because of bovine casein content and structure (L. Hambraeus, E. Forsum and B. Lonnerdal. In: "Food and Immunology", pp 116-124 (Eds. L. Hambraeus, L. A. Hanson and H. McFarlane) Almquist and Wiksell (1977)).
This has led to the production of infant formulas which contain a greater proportion of whey protein, since it is more readily digested by human infants (M. J. Newport and M. J. Henschel, Pediatric Res., 18, 658-662 (1984)), and little or no bovine casein. However, the major protein in whey of cow's milk is beta-lactoglobulin. This protein is essentially absent from human milk and has been determined to be one of the main causes of cow's milk allergy in infants. (I. Axelsson, I. Jakobsson, T. Lindberg and B. Benedikstsson, Acta Pediatrica Scand., 75, 702-707 (1986)). The extent of the problems with allergies to formulas based on cow's milk may be appreciated from the fact that soy-based formulas now comprise a large portion of the human infant formula market in the United States.
Soy-protein formulas, although different in carbohydrate and protein source, are similar in composition to cow's milk-protein formulas following the American Academy of Pediatrics, Committee on Nutrition recommendations for nutrient levels in infant formulas. Differences include a slightly higher protein level and slightly lower carbohydrate content. The protein source is generally soy-protein; the fat is a blend of vegetable oils; and the source of carbohydrate is usually sucrose, corn syrup solids, or a mixture of both. However, the use of soy formulas tends to raise serum alkaline phosphatase and blood urea levels in infants in addition to causing the allergic and digestibility problems encountered with the use of bovine-based protein infant formulas.
Therefore, there exists a present need for a manufacturable human infant formula which comprises a digestible, non-allergenic protein source. Recent research on the activity of human beta-casein has shown that the non-phosphorylated form acts much like human casein in that it precipitates at the calcium ion levels found in mother's milk and binds to the insoluble calcium phosphate just as phosphorylated caseins do (S. M. Sood, P. Chang and C. W. Slattery, Arch. Biochem. Biophys., 264, 574-583 (1988)).
Therefore, proteins which have not been modified post-ribosomally by phosphorylation may be used along with carrageenan to replace the stabilization effects of kappa-casein in infant formula. Thus, providing human infant formulas constituted with purified non-phosphorylated human milk proteins produced by microorganisms (e.g., E. coli or S. cerevisiae) provides a unique answer in solving the inherent digestibility and allergenic problems associated with the use of non-human proteins in human infant formula compositions.
Recombinant DNA techniques may be used to clone cells producing large quantities of the necessary human proteins which may be purified and then combined with carbohydrates, lipids, minerals and sources of non-protein nitrogen to give a simulated human mother's milk formula that does not exhibit the allergenic properties associated with formulas based on cow or other foreign protein. A formula that is nutritionally adequate may be prepared by using only two human proteins: alpha-lactalbumin, which is the major protein of human whey; and beta-casein, the major protein of the casein micelle fraction of human milk. There are a variety of methods for producing these proteins. Representative procedures will be described herein.